Re: md_component_detection = 1

[Christophe Varoqui <christophe.varoqui@free.fr>]

All I can comment is LVM over the multipath implementation from 
Alasdair, RedHat.

For that, you need to set in /etc/lvm/lvm.conf :

    scan = [ "/dev", "/dev/mapper" ]  (you may or may not need this one, 
depending on your distro)
    filter = [ "r/sd.*/", "a/.*/" ]
    types = [ "device-mapper", 254 ]

Here the 254 may vary depending on your setup. To find out for your 
case, do :

[root@cl039 root]# grep mapper /proc/devices
254 device-mapper

Then everything should work as expected :

[root@cl039 root]# multipath -l -v2
red (3600a0b80000b596a000003113d9c5381)
[size=33 GB][features="0"][hwhandler="0"]
\_ round-robin 0 [enabled][first]
  \_ 4:0:3:9 sdan 66:112  [ready ][active]
  \_ 5:0:1:9 sdbh 67:176  [ready ][active]
\_ round-robin 0 [enabled]
  \_ 5:0:3:9 sdcb 68:240  [ready ][active]
  \_ 4:0:1:9 sdt  65:48   [ready ][active]

[root@cl039 root]# pvcreate /dev/mapper/red
  Physical volume "/dev/mapper/red" successfully created

[root@cl039 root]# pvscan
  PV /dev/mapper/red         lvm2 [33.86 GB]
  Total: 1 [33.86 GB] / in use: 0 [0   ] / in no VG: 1 [33.86 GB]


That's the more precise info I can share onn the subject.
Now your on your own.

Regards,
cvaroqui


shahid shaikh wrote:

>
>Hello Chris,
>
>    I have written a sample psuedo driver which is basically consolidating
>multiple paths to LUNs.
>So I need prevent SCSI devices from scanning.
>
>I gone thro' lvm.conf and found out that md is doing the similar thing by
>setting following value in lvm.conf
>
>         md_component_detection = 1
>this parameter, if set, prevents scanning of all the SCSI devices
>contributed in the creation of md.
>
>So is there any parameter in LVM2 or device mapper, setting or clearing
>which can prevent scanning of SCSI devices used for my psuedo driver.
>Obviously other than filtering it out.
>
>Thanks and Regards,
>Shahid Shaikh.
>Software Engineer.
>
>
>
>http://www.patni.com
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